The Role of Nitrogen 13 Ammonia Positron Emission Tomography in Predicting Functional Outcome After Coronary Revascularization

Background: We sought to evaluate the predictive value of positron emission tomography (PET) by using blood flow imaging with semiquantitative data analysis techniques for predicting recovery of regional function after revascularization. Positron emission tomography in combination with fluorodeoxyglucose (FDG) has been shown to predict tissue recovery after revascularization. Previous studies have suggested a quantitative threshold for perfusion as evaluated by PET that separates scar from viable tissue.

Methods And Results: In a group of 25 patients with impaired regional wall motion at baseline as measured by radionuclide ventriculography, we examined the relationship between myocardial blood flow and functional outcome of myocardial segments in patients who underwent coronary revascularization within 2 months after PET. Regional wall motion was graded on a 5-point scale, from normal to dyskinetic. Regional nitrogen 13 (N-13) ammonia uptake values were expressed as a percentage of maximal myocardial N-13 ammonia uptake and compared with values obtained from healthy volunteers. Results were displayed as polar maps, on which regions of interest were placed corresponding to revascularized vascular territories. We were able to show a statistically significant relationship between regional wall motion abnormalities and decreasing blood flow by N-13 ammonia uptake. An N-13 ammonia uptake of greater than 80% for any given segment was highly accurate in predicting normal or nearly normal postoperative regional wall motion, whereas severely decreased ammonia uptake less than 40% showed normalization of regional wall motion in only 13% of segments.

Conclusions: Relative ammonia uptake of greater than 80% and less than 40% preoperatively had excellent predictive value for functional outcome, but intermediate quantitative ammonia uptake (between 40% to 80%) necessitates additional information to accurately predict functional recovery.